Mackenzie Phillips says she had sex with her dad

FILE- This March 5, 1981 file photo shows John Phillips of the pop group 'The Mamas and The Papas,' left, and his daughter MacKenzie, right shown during a taping of the John Davidson Show in Burbank, Calif. Phillips says she had a long-term sexual relationship with her father, John. People magazine says Phillips writes in her new book, "High on Arrival," that she had sex with her father on the night before she was to get married in 1979. (AP Photo/File)
— AP

FILE- This March 5, 1981 file photo shows John Phillips of the pop group 'The Mamas and The Papas,' left, and his daughter MacKenzie, right shown during a taping of the John Davidson Show in Burbank, Calif. Phillips says she had a long-term sexual relationship with her father, John. People magazine says Phillips writes in her new book, "High on Arrival," that she had sex with her father on the night before she was to get married in 1979. (AP Photo/File)
/ AP

"Celebrity Rehab" host Dr. Drew Pinsky told "Extra" that the topic of Phillips' incestuous relationship came up while shooting the upcoming third season of the VH1 reality TV series. Pinksy said he and Phillips talked about the relationship, but out of respect for her family, she told him she did not want those discussions televised.

"What's unusual about Mackenzie's case is there's a romantic quality to the relationship," Pinksy said.

Mackenzie Phillips' book was in the top 20 on Amazon.com as of Wednesday afternoon, but it wouldn't be the first popular book about consensual incest. In 1997, novelist Kathryn Harrison had a best-seller with "The Kiss," a memoir about her affair with her father.

John Phillips, who also had an acknowledged history of drug abuse, co-founded the Mamas and the Papas and helped write its biggest hits, including "California Dreamin'" and "Monday Monday." He also helped organize the 1967 Monterey Pop Festival, which helped introduce Jimi Hendrix to American audiences.